27 August 2010 Optical trapping meets atomic force microscopy: a precision force microscope for biophysics
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Mechanical drift between an atomic force microscope (AFM) tip and sample is a longstanding problem that limits tipsample stability, registration, and the signal-to-noise ratio during imaging. We demonstrate a robust solution to drift that enables novel precision measurements, especially of biological macromolecules in physiologically relevant conditions. Our strategy - inspired by precision optical trapping microscopy - is to actively stabilize both the tip and the sample using locally generated optical signals. In particular, we scatter a laser off the apex of commercial AFM tips and use the scattered light to locally measure and thereby actively control the tip's three-dimensional position above a sample surface with atomic precision in ambient conditions. With this enhanced stability, we overcome the traditional need to scan rapidly while imaging and achieve a 5-fold increase in the image signal-to-noise ratio. Finally, we demonstrate atomic-scale (~ 100 pm) tip-sample stability and registration over tens of minutes with a series of AFM images. The stabilization technique requires low laser power (<1 mW), imparts a minimal perturbation upon the cantilever, and is independent of the tip-sample interaction. This work extends atomic-scale tip-sample control, previously restricted to cryogenic temperatures and ultrahigh vacuum, to a wide range of perturbative operating environments.
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Gavin M. King, Gavin M. King, Allison B. Churnside, Allison B. Churnside, Thomas T. Perkins, Thomas T. Perkins, "Optical trapping meets atomic force microscopy: a precision force microscope for biophysics", Proc. SPIE 7762, Optical Trapping and Optical Micromanipulation VII, 77620D (27 August 2010); doi: 10.1117/12.862745; https://doi.org/10.1117/12.862745

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